1. Field of the Invention
The present invention relates generally to air forming systems, that is, to systems for forming an air laid web on a moving foraminous surface and, more particularly, to systems for uniformly distributing fibers and/or particles to form a web of a predetermined composition. The result is a superior nonwoven product.
2. Description of the Prior Art
From a commercial standpoint, air forming is a relatively young technology and is now finding its way into a wide variety of uses. In most cases, the driving forces for this new and flexible technology have been improved product performance, reduced costs, operating flexibility and environmental considerations. Examples of commercial products that are being produced via air forming which are cost effective and/or embody superior product performance include industrial wipers, disposable hospital underpads, disposable tablecloths and napkins, pre-moistened baby wipes, and adult diapers. Furthermore, as the marketplace demands improved performance and/or reduced costs, it is logical to expect more and better air formed products to appear on the scene.
Some of the economic aspects of air forming which make it attractive include: (1) the ability to locate manufacturing facilities close to the marketplace; (2) economically viable yet smaller units of capacity which result in more moderate capital costs; (3) the simplicity of the operation itself; and (4) the ability to use low cost recycled fiber of the type which can be collected close to the plant site.
According to a simplified description of a conventional air forming process, fibers are carried to a forming head within an airstream generated by transport fans. The raw materials, either virgin or recycled fibers, have been reduced to their fiber form in a hammermill or similar grinding device. By means of a suction box positioned beneath a moving foraminous surface, the fibers carried in the airstream are drawn downwardly onto the surface to form a fibrous web. A suitable binder is added to the fibers at some stage of the process, then cured or otherwise acted upon to impart integrity to the fibrous web. The resulting web can then be treated or converted in various ways to achieve the desired end product.
The growth of air forming has been stimulated by the strengths and limitations of a variety of industries and their influences have affected both product and process advances. Those industries which have had a particularly significant influence on the development of air forming are paper making, textiles, and nonwovens. Being a very mature technology, and utilizing very capital intensive equipment, the papermaking industry has traditionally placed a heavy emphasis on line speed. Since some of the early air forming systems were commercialized by papermaking companies, the technology benefited from the papermakers' bias toward faster and faster line speeds. Additionally, papermakers are particularly fortunate in that they utilize a very low cost raw material, namely, wood pulp. The early use of this low cost raw material in air formed products has been a substantial aid in penetrating new and different markets.
Textile manufacturers have, in effect, set the product standards in areas such as hand, drape and porosity against which nonwoven products are to be measured. Furthermore, the textile and chemical industries have developed a wide array of synthetic fibers which offer improved strength, resistance to rot, ability to be dyed, and ease of being bonded together. Generally speaking, these synthetic textile-type fibers can only be handled by traditional carding, garnetting and other quite mature processes. On the negative side, textile line speeds are slow by the standards of papermaking or nonwoven manufacturing. As a result of the process and product flexibility of air forming systems, nonwovens are now in competition with conventional textile production machinery for the manufacture of products such as disposable generating gowns, surgeon's hand towels, and cubicle curtains.
The major influence of nonwovens on air forming has essentially been twofold. First, the remarkable overall growth in worldwide nonwoven volume has served to stimulate the interest of manufacturers seeking new and better ways to make nonwoven fabrics. Second, the continuing demand for better cost and performance requirements for fabrics within the nonwoven market has led to increasing interest in the flexibility of air forming systems.
The air forming process thus exhibits a number of distinct commercial benefits. Some of the more significant of these are as follows: